In the automated production of contact lenses in general, but especially in the production of large batches of contact lenses, as is the case for example with disposable lenses, it is necessary, at certain stations in the production process, to be able to manipulate the contact lenses safely, quickly and efficiently. An example of such manipulation of a contact lens is when the contact lens is removed from a test cell in which said contact lens has been placed in a liquid, for example in water, in order to test it (e.g. by image processing).
To remove the tested contact lens from such a test cell, devices called grippers are used, as are also used at other stations in such a production process. The contact lens is gripped with the aid of such a gripper and, in the example described above, is removed from the test cell. The contact lens is then deposited for example into a receptacle which can be part of the final package for the contact lens and into which a storage solution (e.g. saline) is dispensed. The receptacle is then welded or sealed with a cover foil, and, after subsequent autoclaving, the final package can be released for distribution.
In the above-described removal of the contact lens from the test cell and the subsequent dispensing of the contact lens into the receptacle in which the saline is present, care must be taken to ensure that only a very small amount of water, preferably none at all, is entrained with the contact lens, otherwise the saline is getting diluted and its osmolarity is changed. This is a problem which is not at all easy to solve, because the contact lens in the above-mentioned test cell has to be sucked from “under water” (with the result that water is necessarily also sucked out with the lens), then transported to the receptacle which is part of the final package, and finally deposited in this receptacle, for which purpose the contact lens has to be released again from the gripper. In addition, the contact lens has to be gripped securely by the gripper (even “under water”), and in the case of small receptacles the contact lens has to be reliably deposited centrally in the receptacle so that it is not later damaged by the cover foil during the welding or sealing of the receptacle.
A gripper suitable to fulfill these requirements is shown in WO 03/080320. The gripper shown there is capable of reliably gripping a contact lens, if appropriate even “under water”, and at the same time ensures that the amount of liquid (e.g. water) entrained is very small (e.g. less than approximately 40 microliters). Also, with this gripper the contact lens can be reliably deposited centrally in a receptacle. As can also be seen, the gripper shown in WO 03/080320 has a plurality of openings in the bearing surface through which suction can be applied, in particular the gripper has a central opening and a plurality of additional openings arranged on an arc of a circle about the central opening. The central opening and each additional opening are connected through respective grooves provided in the bearing surface. The respective groove connecting the central opening with one of the additional openings extends radially outwards beyond the respective additional opening. As underpressure or suction is applied, the contact lens is sucked and adheres to the bearing surface. In addition, water is also sucked up. In case water is trapped between the contact lens and the bearing surface, such water can pass through the grooves to the openings and from there into the interior of the gripper where it will be sucked into the the tube through which the underpressure is applied and is transported away. In case no water is entrapped between the contact lens and the bearing surface or the entrapped water has already been sucked into the tube air is sucked through these channels and openings.
This may sometimes lead to an unwanted drying of the contact lens particularly in the region near the lens edge, which is a crucial region for the wearing comfort. In addition, depending on how the production process is built up it would be desirable to know whether or not a lens has been successfully sucked and adheres to the bearing surface of the gripper head. Moreover, when a contact lens has been successfully sucked and has been transported to its destination location, e.g. to the location where it is intended to be placed into the receptacle of the package, it would later on be desirable to know whether the lens has been successfully released from the bearing surface. Although in the packaging line a separate contact lens presence check may be performed, it may occur that a contact lens has not been released from the gripper despite the application of overpressure thus resulting in a package not containing a lens, so that this package and any additional packages connected thereto must be sorted out and cannot be distributed. In addition, when the gripper has not successfully released the contact lens and subsequently returns to its starting position to grip (suck) another contact lens, it may be unable to grip the next contact lens since the previously gripped contact lens still adheres to the bearing surface. Therefore, it would be desirable to have a clear indication whether or not a contact lens has been successfully sucked and adheres to the bearing surface on one hand and has later on successfully been released from the bearing surface.